The disclosure relates to devices and methods for stabilization of the bony elements of the skeleton. The method and the devices permit adjustment and maintenance of the spatial relationship(s) between neighboring bones. Depending on the specifics of the design, the motion between skeletal segments may be increased, reduced, returned to the normal physiology state or modulated in any desired manner.
Spinal disease is a major health problem in the industrialized world and the surgical treatment of spinal pathology is an evolving discipline. Alteration in the anatomical alignment and physiologic motion that normally exists between adjacent spinal vertebrae can cause significant pain, weakness, deformity and disability. The traditional surgical treatment of abnormal vertebral motion has been the complete immobilization and bony fusion of the involved spinal segments. An extensive array of surgical techniques and implantable devices has been formulated to accomplish this goal.
The growing experience with spinal fusion has shed light on the long-term consequences of vertebral immobilization. It is now accepted that fusion of a specific spinal level will increase the load on, and the rate of degeneration of, the spinal segments immediately above and below the fused level. As the number of spinal fusion operations have increased, so have the number of patients who require extension of their fusion to the adjacent, degenerating levels. The second procedure necessitates re-dissection through the prior, scarred operative field and carries significantly greater risk than the initial procedure while providing a reduced probability of pain relief. Further, extension of the fusion will increase the load on the motion segments that now lie at either end of the fusion construct and will accelerate the rate of degeneration at those levels. Thus, spinal fusion begets additional fusion surgery.
In view of the proceeding, there is a growing recognition that segmental spinal fusion and complete immobilization is an inadequate solution to abnormal spinal motion and vertebral mal-alignment. Correction of the abnormal movement and preservation of spinal mobility is a more intuitive and rational treatment option. It is appropriate to employ motion correction in the initial treatment plan and reserve complete immobilization and fusion for those patients with advanced motion abnormalities that can not be corrected.
Currently, a variety of spinal motion patterns are considered indications of advanced spinal instability. Patients with these motions patterns who develop pain are considered ineligible for treatment strategies that preserve spinal mobility. In particular, aberrant motion at levels of vertebral mal-alignment is considered an indication of disease that can not be corrected with current motion preservation methods. That is, surgeons believe that current motion correction techniques have a limited capacity to support the diseased spinal segments and those spinal segments with vertebral mal-aligned are too unstable to be effectively treated by these techniques. Fusion and complete segmental immobilization remains the main surgical option for the surgical treatment of these patients.
The current limitations of motion preservation techniques needlessly relegate a large number of patients to fusion surgery and the numerous disadvantages of complete spinal immobilization. A method for the treatment of segments with aberrant motion and/or spinal mal-alignment without fusion is clearly needed. It would correct the abnormal motion and preserve mobility in a significant number of patients who must currently undergo spinal fusion.